Dual-Phase Acid-Based Fracturing Composition with Corrosion Inhibitors and Method of Use Thereof

ABSTRACT

A dual-phase acid-based fracturing composition with corrosion inhibitors and method for use in acid-based matrix and fracturing operations in oil and gas wells is provided. The composition includes an acid, a hydrocarbon, a hydrocarbon-soluble corrosion inhibitor, an acid-soluble corrosion inhibitor, and an acid-soluble inhibitor aid.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/864,776, filed Jan. 8, 2018, which is a continuation of U.S. patentapplication Ser. No. 14/830,419, filed Aug. 19, 2015, which is adivisional of U.S. patent application Ser. No. 13/682,405, filed Nov.20, 2012, which claims priority to U.S. Provisional Patent ApplicationNo. 61/563,287, filed Nov. 23, 2011, the disclosures of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to a composition and method for inhibitingcorrosion during acid stimulation treatments in oil and gas wells. Morespecifically, the invention relates to a fluid composition and method ofusing the fluid composition to coat the metal tubing and downholeequipment of the well during both the injection and the flowback phases.

BACKGROUND OF THE INVENTION

During well operations, “matrix acidizing” and “acid fracturing” methodsare employed to enhance the productivity of hydrocarbon wells. Ingeneral, acid or acid-based fluids are injected into the well tubing(the “injection phase”) and into the formation rock. These acidsdissolve or partially dissolve the formation rock, creating alternativeflow paths for hydrocarbons. After the acids are “spent” in theformation rock, they are returned to the surface through the same welltubing during the “flowback phase”.

One of the difficulties encountered when acid-based fracturing methodsare employed is that most of the well tubing and downhole equipment ismade of metal. In traditional acid-based fracturing methods utilized inoil wells, particularly as temperatures and pressures increase, theinjected acids are corrosive to the metal tubing and the downholeequipment. To help prevent this, corrosion inhibitors are typicallyadded to the acids. The corrosion inhibitors act to coat the metal andminimize the corrosive effects of the acids. As temperatures andpressures increase, acid reactivity also increases and increased amountsof inhibitor are needed to compensate for the increased reactivity.

Another difficulty encountered in typical acid-based fracturing methodsis that after the acid is “spent”—injected into the formation rock foracid fracturing purposes—the acid still retains corrosive propertiesthat will damage metal on its return to the surface during the “flowbackphase”. Most prior art corrosion inhibitors work by coating the metaltubing during the “injection phase,” and the inhibitors typically arethen consumed during this phase of the operation. After the acids havepassed through the formation rock, little to no inhibition content isavailable to protect the well equipment during the “flowback phase” ofthe operation.

The cost of corrosion inhibitors in acid-based operations is a majorcontributor to the overall cost of the fracturing operation. Because oftheir corrosive properties, the most effective acids for fracturingrequire inhibitor dosages that lie outside of economic feasibility.Additionally, the “spent acids” can damage the well equipment during the“flowback phase”. Therefore, it would be advantageous to use acomposition capable of protecting the well equipment, including pipes,electric submersible pumps (ESPs), and other downhole tools, in both theinjection and flowback phases.

SUMMARY OF THE INVENTION

The present invention provides for a dual-phase acid-based fracturingcomposition with corrosion inhibitors and method for mixing and usingthe composition such that the metal parts of the well tubing anddownhole equipment are protected from the corrosive effects of the acid,during both the injection and flowback phases. The composition consistsof a dual-phase acid-in-hydrocarbon emulsion, with a separate corrosioninhibitor present in each of the different phases. When the compositionis injected into the formation rock during the “injection phase”, thehydrocarbon-soluble corrosion inhibitor coats the interior of the metaltubing, forming a protective film. The acid-soluble corrosion inhibitorremains present in the acid fluids during the injection phase and thestimulation of the formation, and is not spent until the flowback phase.

In one aspect, the dual-phase acid-based fracturing composition includesan acid, a liquid hydrocarbon, an emulsifier, a hydrocarbon-solublecorrosion inhibitor, and an acid-soluble corrosion inhibitor. Thecombination of the acid, the liquid hydrocarbon, the emulsifier, thehydrocarbon-soluble corrosion inhibitor, and the acid-soluble corrosioninhibitor is operable to protect the metal tubing and equipment of anoil and gas well during both the injection and flowback phases ofacid-based fracturing operations.

In certain embodiments, the acid can be selected from HCl (hydrochloricacid) and is present in concentrations ranging up to about 28% by weightand present in the emulsion in concentrations ranging from about 50-80%by volume. In certain embodiments, the hydrocarbon can be alow-viscosity, low-sulfur diesel, alternatively having a diesel mixturethat includes hydrocarbons ranging between about 10-15 carbon atoms. Inalternative embodiments, the hydrocarbon-soluble inhibitor can bepresent in concentrations ranging from about 0.01 to 3% by volume,relative to the amount of hydrocarbon present in the composition, andthe acid-soluble inhibitor can be present in concentrations ranging fromabout 0.01 to 3% by volume, relative to the acid present in thecomposition. In other embodiments, the acid can include at least onestrong acid at any concentration, and the hydrocarbon can be any liquidhydrocarbon with more than 5 carbon atoms.

In one aspect, the present invention relates to a method of preparing acorrosion inhibiting fracturing composition. The corrosion inhibitingcomposition includes a dual-phase acid-in-hydrocarbon emulsion with twocorrosion inhibitors, such that a hydrocarbon-soluble corrosioninhibitor is present in the hydrocarbon phase, and an acid-solubleinhibitor is present in the acid phase. The method includes the steps ofpreparing the hydrocarbon phase and the acid phase separately beforemixing with an emulsifier. In one embodiment, the emulsifier can be anamine-based surfactant. In certain embodiments, the emulsifier isdissolved in an organic solvent.

In one embodiment, the hydrocarbon phase can be prepared by adding theemulsifier and the hydrocarbon-soluble corrosion inhibitor to thehydrocarbon in a mixing device. In other embodiments, the hydrocarbonphase can be prepared by any mixing technique. The acid phase can beprepared by adding an acid-soluble corrosion inhibitor to the acid.

In one embodiment, an acid-soluble corrosion inhibitor aid is added tothe acid phase in concentrations ranging between about 0.1 to 3% byvolume, relative to the amount of acid present in the composition.

In one embodiment, the acid-in-hydrocarbon emulsion is prepared byadding the acid phase to the emulsified hydrocarbon drop wise, at aconstant speed, to ensure the emulsion is uniform. In other embodiments,the acid can be added to the hydrocarbon using any mixing technique.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides scanning electron microscope analysis of the surface ofa metal coupon after being treated with the dual-phase corrosioninhibitor during the injection phase according to embodiments of thepresent invention.

FIG. 2 provides scanning electron microscope analysis of the surface ofa metal coupon after being treated with the “spent” acid, during theflowback phase according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Although the following detailed description contains many specificdetails for purposes of illustration, it is understood that one ofordinary skill in the art will appreciate that many examples, variationsand alterations to the following details are all within the scope andspirit of the invention. Accordingly, the exemplary embodiments of theinvention described herein are set forth without any loss of generality,and without imposing limitations, relating to the claimed invention.

The present invention addresses problems associated with prior artmethods and compositions used in acid-based fracturing operations toeffectively fracture the formation rock while at the same timepreventing acid corrosion in oil and gas wells.

As used herein, “formation” and “formation rock” refer to the rockaround the borehole of an oil and gas well, including formationscomprised of calcium carbonate rock.

The dual-phase acid-based fracturing composition described hereingenerally includes an acid, a liquid hydrocarbon, an emulsifier, ahydrocarbon-soluble corrosion inhibitor, and an acid-soluble corrosioninhibitor. In addition to being used for fracturing the formation rock,the composition fluids form a protective film that coats metal tubingand downhole equipment during both the injection and flowback phases ofacid fracturing operations. Therefore, in certain embodiments, thedual-phase acid-based fracturing composition fluids exist in anacid-in-hydrocarbon emulsion, with a separate corrosion inhibitorpresent in each phase. In the injection phase, the dual-phase acid-basedfracturing composition is injected into the formation rock. Duringinjection, the hydrocarbon-soluble corrosion inhibitor present in thecomposition acts to coat the interior of the metal tubing and downholeequipment, protecting their surfaces from the corrosive effects of theinjected acid. After injection, the composition enters the formationrock to part or open fractures in the formation and to etch pathways inthe formation rock. The acid-soluble corrosion inhibitor remains presentin the acid fluids during injection and is not spent until the flowbackphase.

In one aspect, the present invention is directed to a dual-phaseacid-based fracturing composition that includes at least two corrosioninhibitors for use in fracturing the formation rock while alsopreventing the corrosion of metal tubing and downhole equipment in thewells. In certain embodiments, the composition exists as a dual-phaseacid-in-hydrocarbon emulsion. Advantageously, the dual-phase compositionincludes at least two separate corrosion inhibitors, at least onepresent in the acid phase, and at least one present in the hydrocarbonphase.

As used herein, “acid” refers to any group of strong acids that ionizecompletely in an aqueous solution by losing one proton. Furthermore,“acid fracturing operations” refers to the process of using acid to partor open fractures in formation rock and to etch pathways along thefractures, for the purpose of increasing rock permeability near thewellbore. When the acid comes into contact with the metal tubing andequipment present in the well, corrosion of the metal occurs.

As used herein, “corrosion inhibitor” refers to a chemical additive usedin acid-based treatments to protect metal components in the wellbore andtreating equipment from the corrosive effects of the acid fluids. Asused herein, corrosion inhibitors generally adsorb on the metal surfaceand form a protective film.

As used herein “spent acid” refers the composition fluids that remainafter the composition has reacted with formation rock.

As used herein, “injection phase” refers to the first phase of acidfracturing operations, in which the acid-based composition fluids arefirst injected into the well tubing, before they reach the formationrock. Additionally, “flowback phase” refers to the last phase of acidfracturing operations in which fluids that remain in the formation rockafter acid fracturing return back up the metal tubing, towards thesurface of the well.

In certain embodiments, the corrosion inhibitor present in thehydrocarbon phase is used during the injection phase to coat and protectthe metal tubing and well equipment. The corrosion inhibitor present inthe acid phase is not generally used or spent during the injectionphase, and is available to form the protective coating on the metaltubing and equipment during the flowback phase.

In certain embodiments, the hydrocarbon can be selected from any classof liquid hydrocarbons having more than 5 carbon atoms, alternatively ina range of about 10-15 carbon atoms, or in a range of about 15-20 carbonatoms. Certain hydrocarbons for use in the present invention can includediesels and low-sulfur diesels. The hydrocarbon-soluble corrosioninhibitor can be present in the hydrocarbon phase in an amount whichranges between about 0.01% to 3% by volume, relative to the amount ofhydrocarbon present. In certain embodiments, the hydrocarbon-solublecorrosion inhibitor can be obtained from a commercial supplier. Incertain embodiments, the hydrocarbon-soluble corrosion inhibitor can bean alcohol based inhibitor such as COAT-B1400 (Nalco Champion, Houston,Tex.). In other embodiments, the hydrocarbon-soluble corrosion inhibitorcan be selected from standard methanols.

In certain embodiments, the emulsifier selected can be an anime-basedsurfactant dissolved in an organic solvent. “Amine-based surfactant”refers to a group of cationic surfactants that have a positively chargedhead group. The emulsifier can be present in the composition by about0.05 to 1.5% by volume, relative to the volume of the hydrocarbonpresent. In certain embodiments, the emulsifier can be anemulsified-acid additive such as the U108 emulsifier (SchlumbergerTechnology Corporation, Sugar Land, Tex.). In other embodiments, theemulsifier can be a cationic surfactant selected from a group of linearalkyl-amines and alkyl-ammoniums.

The acid can include one or more members selected from the group ofstrong acids. The acid component of the dual-phase acid-based fracturingcomposition will typically be present in high concentrations, such asabout 50-80% by volume of the composition. In certain embodiments, theacid can be highly concentrated hydrochloric acid (HCl).

The acid-soluble corrosion inhibitor can be obtained from a commercialsupplier and can be present in the acid phase in an amount which rangesbetween about 0.01 to 3% by volume, relative to the amount of acidpresent. In certain embodiments, the acid-soluble inhibitor is corrosioninhibitor such as the A262 inhibitor (Schlumberger TechnologyCorporation, Sugar Land, Tex.). In certain embodiments, the acid-solublecorrosion inhibitor does not have surfactant properties.

In certain embodiments, an acid-soluble corrosion inhibitor aid can beadded to the acid phase. The inhibitor aid can be selected from acommercial supplier and can be present in the acid phase in an amountwhich ranges between 0 and 3% by volume. If used, in certainembodiments, the inhibitor aid can be the A201 inhibitor aid(Schlumberger Technology Corporation, Sugar Land, Tex.). In otherembodiments, the inhibitor aid can be selected from formic acid.

In another aspect, the present invention provides a method for making adual-phase acid-based fracturing composition such that anacid-in-hydrocarbon emulsion with two corrosion inhibitors is prepared.In certain embodiments, the two phases are prepared separately and thenmixed together. To prepare the acid phase according to the presentinvention, an acid is chosen and diluted with treatment water to anoperable concentration. An acid-soluble corrosion inhibitor is thenselected and added to the acid and mixed thoroughly to produce the acidphase of the emulsion. In certain embodiments, an inhibitor aid can beadded to the acid phase in order to increase the effectiveness of theacid-phase inhibitor during the flowback phase of acid based fracturingoperations.

To prepare the hydrocarbon phase, an amine-based emulsifier is selectedand then dissolved in an organic solvent such as acetone or methanol. Aliquid hydrocarbon is selected to which the emulsifier is added untilthe two compounds are thoroughly mixed. A hydrocarbon-soluble corrosioninhibitor is then selected and added to the liquid hydrocarbon toproduce the emulsified hydrocarbon phase. The acid phase is then addedto the emulsified hydrocarbon phase.

The acid phase and the emulsified hydrocarbon phase of the presentinvention are combined and mixed, preferably drop wise. Adding the acidphase to the hydrocarbon phase drop wise creates a more uniformacid-in-hydrocarbon emulsion and produces the highest amount ofinhibition activity in the composition of the present invention. Inother embodiments, the acid phase and the hydrocarbon phase can be mixedtogether at once and shaken by hand.

The mixing of the acid phase and hydrocarbon phase produces a dual-phaseacid-in-hydrocarbon emulsion with two corrosion inhibitors. In certainembodiments, the acid-in-hydrocarbon emulsion is not a microemulsion.

In certain embodiments, the dual-phase acid-in-hydrocarbon emulsion canthen be used in acid fracturing operations to fracture the formationrock while at the same time protecting the metal tubing and equipment inoil wells during both the injection and flowback phases.

In certain embodiments, the composition and methods described herein areeffective for protecting tubulars, including steel corrosion resistantalloys such as Chrome 13 (13Cr; Hamilton Metals, Houston, Tex.) andsuperchrome tubing during acid fracturing operations employing highlycorrosive strong acids.

In certain embodiments, the composition and methods described herein areeffective for the protection of metal tubing and downhole equipmentduring acid fracturing operations employing concentrated hydrochloricacid (HCl); such as HCl solutions greater than 20% concentration byweight, or alternatively greater than about 25% concentration by weight.

In another embodiment, the dual-phase acid-based fracturing compositionwith two corrosion inhibitors can be injected into a formation. Incertain embodiments, the hydrocarbon-soluble corrosion inhibitor forms aprotective film on the metal tubing and downhole equipment of the oiland gas well. In certain embodiments, the hydrocarbon-soluble corrosioninhibitor film protects the metal tubing and downhole equipment from thecorrosiveness of the acid in the composition during the injection phase.In certain embodiments, the acid-soluble corrosion inhibitor remainsdissolved in the dual-phase acid-based fracturing composition.

In one embodiment, the dual-phase acid-based fracturing compositiondescribed herein is injected into the formation rock and the acidfunctions to dissolve, part or open fractures in the formation rock. Incertain embodiments, once the acid has been “spent” in the formationrock, it can come back into contact with the metal tubing and downholeequipment in the oil and gas well. In one embodiment, the acid-solublecorrosion inhibitor can form a protective film on the metal tubing anddownhole equipment. In certain embodiments, the acid-soluble corrosioninhibitor film protects the metal tubing and downhole equipment from thecorrosiveness of the acid in the composition during the flowback phase.

EXAMPLES

The examples below used certain exemplary dual-phase acid-in-hydrocarbonemulsions, as described herein.

Example 1

The corrosion inhibiting properties of two acid-in-hydrocarboncompositions were compared by immersing a metal coupon in eachcomposition and measuring the amount of metal corrosion. Two dual-phaseacid-in-hydrocarbon emulsions were prepared—one with two corrosioninhibitors as described herein, and one with one corrosion inhibitor inthe acid phase only. Two metal coupons were immersed in both emulsionsat 130° Celsius and 700 psi for approximately 6 hours. After immersion,the weight loss of both coupons was measure and calculated. The weightloss of the metal was reduced by at least about 50% when two corrosioninhibitors were used as compared to one. Table 1 provides a comparisonof the corrosion inhibition of an exemplary dual-phaseacid-in-hydrocarbon emulsion against a composition that includes onlyone corrosion inhibitor present in the acid phase.

TABLE 1 Temper- Pressure 700 psi Temper- Pressure 700 psi ature: 130 °C.ature: 130 °C. Two corrosion inhibitors, in Corrosion inhibitor in acidonly hydrocarbon and acid phases Weight before 37.3826 Weight before38.0302 soaking, g soaking, g Weight after 37.2209 Weight after 37.9478soaking, g soaking, g Weight loss, g 0.1617 Weight loss, g 0.0824 Weightloss, % 0.43% Weight loss, % 0.21%

Example 2

Two metal coupons were immersed in freshly prepared dual-phaseacid-in-hydrocarbon emulsions. FIG. 1 shows a scanning electronmicroscope analysis of the surface of the metal coupon after immersion.The analysis of the fluid composition left on the metal shows that onlythe hydrocarbon-soluble corrosion inhibitor was used.

Example 3

Two metal coupons were immersed, the first in freshly prepareddual-phase acid-in-hydrocarbon emulsion with two corrosion inhibitors,and the second in spent dual-phase acid-in-hydrocarbon emulsion with twocorrosion inhibitors. The acid was spent by adding calcium carbonate tofreshly prepared dual-phase acid-in-hydrocarbon emulsion with doublecorrosion inhibition. FIG. 1 and FIG. 2 show the scanning electronmicroscope analysis of both metal coupons. The availability of nitrogenin FIG. 2 shows that the metal coupon was coated with an aqueousamine-based corrosion inhibitor. FIG. 1 does not show nitrogen in theanalysis which shows that the hydrocarbon-soluble corrosion inhibitorwas coating the metal coupon. These results show the role of eachcorrosion inhibitor in each phase.

Examples 1 and 2 show that in an acid fracturing operation, if thepresent invention is utilized as described herein, thehydrocarbon-soluble corrosion inhibitor provides protection against thecorrosion of the metal tubing and downhole equipment from the acidduring the injection phase. The acid-soluble corrosion inhibitor willremain in the injected fluids. After the acid is injected into theformation rock and becomes “spent”, the acid-soluble corrosion inhibitorremains available to protect the metal tubing and downhole equipmentduring the flowback phase of acid-based fracturing operations.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions, and alterations canbe made hereupon without departing from the principle and scope of theinvention. Accordingly, the scope of the present invention should bedetermined by the following claims and their appropriate legalequivalents.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

Throughout this application, where patents, other products, orpublications are referenced, the disclosures of these references intheir entireties are intended to be incorporated by reference into thisapplication, in order to more fully describe the state of the art towhich the invention pertains, except when these reference contradict thestatements made herein.

That which is claimed is:
 1. A dual-phase acid-based fracturingcomposition for use in matrix acidizing and acid-fracturing operationsin oil and gas wells for the prevention of corrosion of well tubing anddownhole equipment, the composition comprising; a strong acid operableto be diluted with treatment water and to dissolve formation rock; aliquid hydrocarbon comprising 5 or more carbon atoms; an emulsifierselected from the group consisting of an amine-based surfactant, linearalkyl amines and alkyl ammoniums; a hydrocarbon-soluble corrosioninhibitor present in a hydrocarbon phase of the composition, thehydrocarbon-soluble corrosion inhibitor comprising an alcohol; and anacid-soluble corrosion inhibitor present in an acid phase of thecomposition; where the strong acid during acid-based oil well operationsforms a spent acid upon dissolving formation rock, where the compositionis operable to coat metal tubing and well equipment with thehydrocarbon-soluble corrosion inhibitor such that the metal tubing andwell equipment is protected from the acid during an injection phase, andwhere the composition is operable to coat the metal tubing and wellequipment with the acid-soluble corrosion inhibitor such that the metaltubing and well equipment is protected from the spent acid during aflowback phase.
 2. The dual-phase acid-based fracturing composition ofclaim 1, wherein the strong acid is present in a concentration between20% and 28% by weight.
 3. The dual-phase acid-based fracturingcomposition of claim 1, wherein the emulsifier is present inconcentrations in a range of from 0.05% to 1.5% by volume relative tothe amount of the liquid hydrocarbon in the composition.
 4. Thedual-phase acid-based fracturing composition of claim 1, wherein thehydrocarbon-soluble corrosion inhibitor present in a range of 0.01% to3% by volume relative to the amount of the liquid hydrocarbon in thecomposition.
 5. The dual-phase acid-based fracturing composition ofclaim 1, wherein the acid-soluble corrosion inhibitor is present in anamount of up to 3% by volume relative to the amount of acid in thecomposition.
 6. The dual-phase acid-based fracturing composition ofclaim 1, wherein the liquid hydrocarbon comprises hydrocarbons rangingbetween about 10-15 carbon atoms.
 7. The dual-phase acid-basedfracturing composition of claim 1, wherein the liquid hydrocarboncomprises diesel.
 8. The dual-phase acid-based fracturing composition ofclaim 1, wherein the liquid hydrocarbon comprises a diesel mixture thatincludes hydrocarbons ranging between about 10-15 carbon atoms.
 9. Thedual-phase acid-based fracturing composition of claim 1, wherein thestrong acid is hydrochloric acid.
 10. The dual-phase acid-basedfracturing composition of claim 1, wherein the acid is present in anamount between 50%-80% by volume relative to the total volume of thecomposition.
 11. The dual-phase acid-based fracturing composition ofclaim 1, wherein an acid-soluble corrosion inhibitor aid comprisingformic acid is present in the acid in concentrations between 0.01% to 3%by volume relative to the amount of acid in the composition.
 12. Thedual-phase acid-based fracturing composition of claim 1, wherein theacid-soluble corrosion inhibitor remains dissolved in the composition.13. The dual-phase acid-based fracturing composition of claim 1, whereinthe composition reduces weight loss in metal tubing and well equipment.